The ancient African rice that could help farmers grapple with climate change

Put the two plants side by side and the untrained eye would struggle to tell them apart. 

“They’re going to look very similar to each other, but they evolved differently,” Michael Purugganan, a New York University evolutionary biologist who has spent years studying the domestication of rice, told RFI. 

Asian rice, Oryza sativa, was domesticated along China’s Yangtze River around 9,000 years ago – thousands of years before West African farmers domesticated Oryza glaberrima, Purugganan said. 

Yet far less is known about how that second domestication happened. 

“We don’t know as much as we do about Asian rice, largely because the archaeology in that part of the world is not as well developed as in Asia,” Purugganan explained. 

Genetic research into the crop’s history has also gathered pace only in recent years. African rice largely remained in West Africa, although some crossed the Atlantic with enslaved Africans and was grown for a time in the Americas. 

Asian rice followed a very different path. It spread around the world and eventually came to dominate even in Africa, where it increasingly replaced the indigenous crop farmers had developed. 

There were practical reasons for the shift. African rice can be frustrating to harvest, shedding ripe grain before it can be collected and collapsing in the field as its stems weaken late in the growing season. 

But the plant held on in some of West Africa’s most difficult growing environments, including dry uplands and areas of deep water, said Koichi Futakuchi, a veteran rice scientist at the Africa Rice Centre, a pan-African research body based in Cote d’Ivoire.  

Scientists have recognised its potential for decades. One African rice line, CG14, “possesses resistance to multiple stresses in Africa such as iron toxicity, drought, deep water, striga [a parasitic weed] and nematodes [microscopic worms that attack roots]”, Futakuchi said. 

The challenge has been getting more of those qualities into Asian rice. 

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Early riser

One particularly useful trait comes down to something surprisingly simple – what time of day the plant flowers. 

Rice is particularly vulnerable to extreme heat when it flowers, and some types of African rice flower early in the morning, before temperatures climb later in the day. 

Futakuchi and his colleagues screened 2,093 African and Asian rice samples in Benin and Nigeria. 

A total of 64 flowered early across different years, seasons and locations. Of those, 15 samples showed more than 80 percent of their flowering before 9am, making them candidates for breeding rice that can escape the worst of heat stress. 

Early-morning flowering itself is not a new discovery. The trait was identified in a few African rice lines in the 1970s, Futakuchi said. What is relatively new is the broader push to look beyond Asian rice for genes that could improve it. 

“It’s only been in the last 10 or 15 years that people have been thinking about getting genes from wild rice species into Asian rice, and now from other domesticated species, such as African rice, into Asian rice,” Purugganan said. 

This possibility drove his own research.  
“My interest in African rice stemmed from the idea that in African rice, we may have genes that can help improve Asian rice, especially in adapting to much more stressful environments.”  

Putting that idea into practice is complicated. Breeders need to capture the useful traits of African rice without carrying across the characteristics that made it less attractive to farmers in the first place.  A bag of rice in the Casamance village of Niaguis, Senegal, 7 March 2024.

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New Rice for Africa 

Scientists have already succeeded in bringing the two species together. 

In the 1990s, a team led by Sierra Leonean plant breeder Monty Jones at the West Africa Rice Development Association, or WARDA, crossed African and Asian rice to create what became Nerica – New Rice for Africa.  

Jones shared the 2004 World Food Prize for the work. AfricaRice said 82 Nerica varieties have since been developed: 18 for upland cultivation, 60 for rainfed lowlands and four for irrigated environments. 

But simply crossing an African rice plant with an Asian one can be difficult. Depending on which plants are paired, the result may be only a few seeds – or none at all – Futakuchi explained. 

Creating Nerica also required a technique known as embryo rescue, in which hybrid embryos are removed and grown in the laboratory so they can survive. 

“Even though you can cross Asian and African rice, it’s not an easy cross to make,” Purugganan said. “You still get some infertility.” 

All the upland Nerica varieties use the same African rice line, CG14, as a parent, while all the lowland varieties use another, TOG5681, Futakuchi said. 

The offspring were then bred back twice with Asian rice. Backcrossing works well when breeders want to transfer one useful African trait, but the resulting plants become increasingly like the Asian species. 

“Such high adaptability to African environments cannot be brought to Oryza sativa with the backcrossing approach,” Futakuchi said. 

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Spear, shield and armour 

New research from China has uncovered one reason those crosses can fail.  

A team at Nanjing Agricultural University recently reported in the journal Science that it had discovered one reason African and Asian rice can struggle to produce fertile offspring when they are crossed. 

While the biology may be complicated, the basic idea isn’t.  

The system has three parts – a toxin and two antidotes – that work rather like a spear, a shield and a suit of armour. The toxin acts as the spear, attacking reproductive cells that lack the right protection, while the two antidotes act as the shield and armour, defending against the attack. 

The result is a genetic contest inside the plant. Reproductive cells without the right genetic protection can be destroyed, while protected cells survive and are more likely to pass their genes to the next generation. 

Identifying that system does not mean scientists have overcome every barrier between the two species. Other causes of sterility remain, and the research has not yet produced a new variety of rice ready for farmers to plant. 

For breeders, this could open up much more of African rice. Futakuchi believes they could “exploit a wider range” of the crop and use more of its useful traits without repeatedly crossing the offspring back with Asian rice. 

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The potential pool is vast. AfricaRice maintains more than 4,000 genetically distinct samples of African rice – the world’s largest collection. 

Scientists are already screening them for traits that could help rice withstand difficult growing conditions, as well as for nutritional qualities including protein and micronutrients. Futakuchi said the new discovery could accelerate that work. 

That could be particularly valuable in Africa, where much of the rice crop depends on rainfall and can face several pressures at once. Better use of African rice could also help the continent move towards rice self-sufficiency. 

Asked who stood to benefit, Futakuchi said: “Of course, farmers in Africa.”